In gasoline engines, diesel engines, and other internal combustion engines mounted to, for example, vehicles, various improvements have been made, for example, to increase engine output and reduce exhaust gas emission (e.g., NOx) by controlling multiple control quantities (e.g., amount of injected fuel) based on the measurement (intake air volume) of the volume of air sucked into the combustion chamber (i.e., into a cylinder). An air flow meter, located in an intake air path, is used to measure the intake air volume in such control (engine control) of an internal combustion engine (see, for example, Patent Document 1).
To measure an intake air volume using an air flow meter, for example, an output signal of the air flow meter is acquired and fed at predetermined time intervals (e.g., every 4 msec) (acquired and fed time-synchronously) to an ECU (electronic control device) to calculate successive averages (average flow rates of the intake air) of sampling values (hereinafter, may be referred to as AFM data) of the output signal (hereinafter, may be referred to as the AFM signal) of the air flow meter at predetermined intervals. The average flow rates of the intake air thus calculated are used to control the internal combustion engine (e.g., to control the amount of injected fuel).